Shouquan Li

Improved hydrogen storage properties of MgH2 by ball milling with AlH3: preparations, de/rehydriding properties, and reaction mechanisms

Organometallically prepared AlH3 and as-received Al powders were mixed with MgH2 to improve the dehydriding and rehydriding properties of MgH2. Thermal analysis shows that the onset dehydriding temperature of MgH2 is reduced by 55 °C (or 25 °C) when mixed with AlH3 (or Al). The destabilization of MgH2 is attributed to the formation of Mg–Al alloys through the reaction between MgH2 and Al. Isothermal dehydriding measurements demonstrate that AlH3 and Al both improve the dehydriding kinetic of MgH2 to some extent, and it only takes 44 min for MgH2 + AlH3 (5.4 h for MgH2 + Al) to release 60% of the hydrogen of MgH2 at 300 °C, but 8.6 h are required for as-milled MgH2. The apparent activation energy for the dehydriding of MgH2 is reduced from 174.6 kJ mol−1 for as-milled MgH2 to 154.8 and 138.1 kJ mol−1 for MgH2 mixed with Al and AlH3 respectively; this is responsible for the improvement in the dehydriding kinetics of MgH2. Despite this, AlH3 is better in destabilizing MgH2 than the as-received Al for the fact that Al* formed in situ from the decomposition of AlH3 is oxide-free on the particle surfaces, which effectively increases the chemical activity of Al*. Furthermore, the brittleness of AlH3 makes it easier to mix MgH2 with AlH3, which would result in uniform distributions of Mg and Al and shortening of the diffusion length. Concerning the reversibility, at 300 °C and 5 MPa H2 and MgH2 are fully recovered in the dehydrided MgH2 + Al, and MgH2 + AlH3 samples after rehydriding for 10 h. The rehydriding kinetic of MgH2 is significantly enhanced for the dehydrided MgH2 + AlH3, but not in the case of the MgH2 + Al.

Active species of CeAl4 in the CeCl3-doped sodium aluminium hydride and its enhancement on reversible hydrogen storage performance

By directly doping CeAl(4) into sodium aluminium hydride, which probably serves as the active species in the hydriding and dehydriding processes of CeCl(3)-doped NaAlH(4), a high reversible hydrogen capacity of 4.77-4.92 wt% (close to expected capacity of 5.13 wt%) can be achieved in less than 20 min under moderate conditions.

In situ synthesis of SnO2 nanoparticles encapsulated in micro/mesoporous carbon foam as a high-performance anode material for lithium ion batteries

SnO2 has high capacity but poor cycling stability for Li-ion batteries due to pulverization and aggregation. Herein, we tackle these two challenges by uniformly dispersing carbon coated nanoSnO2 into a micro-sized porous carbon matrix to form a nano-SnO2/C composite anode using a facile and scalable in situ synthesis strategy. The SnO2@C nanocomposite exhibits a capacity of 640 mA h g−1 at 500 mA g−1 in the initial 150 cycles and then increases to 720 mA h g−1 and maintains this capacity for 420 cycles. The superior electrochemical performance with long cycle lifetimes of the carbon foam–SnO2 nanocomposites could be attributed to their unique carbon microstructures: the network of carbon sheets provides favorable electron transport, while the interconnected micro-/mesopores can serve as the effective channels of lithium ion transport, thereby supplying short lithium ion diffusion pathways. Meanwhile, these pores surrounding the active species of nanoSnO2 along with flexible carbon nanosheets can accommodate the severe volume variations during prolonged electrochemical cycling and mitigate the Sn aggregation. The present study provides a large-scale synthesis route to synthesize SnO2-based anode materials with superior electrochemical performance for lithium ion batteries.

Carbon encapsulated 3D hierarchical Fe3O4 spheres as advanced anode materials with long cycle lifetimes for lithium-ion batteries

As anode materials for lithium ion batteries, metal oxides have large storage capacity. However, their cycle life and rate capability are still not suitable for commercial applications. Herein, 3D hierarchical Fe3O4 spheres associated with a 5–10 nm carbon shell were designed and fabricated. In the constructed architecture, the thin carbon shells can avoid the direct exposure of encapsulated Fe3O4 to the electrolyte and preserve the structural and electrochemical integrity of spheres as well as inhibit the aggregation of pulverized Fe3O4 during electrochemical cycling. The hierarchical structure formed by the bottom-up self-assembly approach can efficiently accommodate the mechanical stress induced by the severe volume variation of Fe3O4 during lithiation–delithiation processes. Moreover, the carbon shell together with the structure integrity and durability endows the favorable high conductivity and efficient ion transport. All these features are critical for high-performance anodes, therefore enabling an outstanding lithium storage performance with a long cycle lifespan. For instance, such an electrode could deliver a capacity of 910 mA h g−1 even after 600 cycles with a discharge–charge rate of 1 A g−1. In addition, this effective strategy may be readily extended to construct many other classes of hybrid electrode materials for high-performance lithium-ion batteries.

Novel AgPd hollow spheres anchored on graphene as an efficient catalyst for dehydrogenation of formic acid at room temperature

Highly dispersed AgPd hollow spheres anchored on graphene (denoted as AgPd-Hs/G) were successfully synthesized through a facile one-pot hydrothermal route for the first time. The fabrication strategy was efficient and green by using L-ascorbic acid (L-AA) as the reductant and trisodium citrate dihydrate as the stabilizer, without employing any seed, surfactant, organic solvent, template, stabilizing agent, or complicated apparatus. The as-synthesized AgPd-Hs/G catalyst exhibits a sphere-shaped hollow structure with an average diameter of about 18 nm and a thin wall of about 5 nm. The hollow architecture with a thin wall and excellent dispersion on the graphene ensure that most of the atoms are located on the surface or sub-surface, which provides reactive catalytic sites for the dehydrogenation of formic acid. Therefore, a superior catalytic effect was achieved compared with other catalysts such as Pd/G and AgPd/C. The as-synthesized AgPd-Hs/G exhibits a catalytic activity with an initial turnover frequency (TOF) value as high as 333 mol H2 mol−1 catalyst h−1 even at room temperature (25 °C) toward the decomposition of formic acid. The present AgPd-Hs/G with efficient catalysis on the dehydrogenation of formic acid without any CO generation at room temperature can pave the way for a practical liquid hydrogen storage system and therefore promote the application of formic acid in fuel cell systems.

Synergistically thermodynamic and kinetic tailoring of the hydrogen desorption properties of MgH2 by co-addition of AlH3 and CeF3

MgH2 possesses a high hydrogen capacity and excellent reversibility. However, the high thermal stability and slow sorption kinetics retard its practical application as an on-board hydrogen storage material. In this work, AlH3 and CeF3 were introduced into Mg-based materials for the purpose of improving both the thermodynamic and the kinetic properties of MgH2. DSC-TG analysis shows that the onset hydrogen desorption temperature of MgH2 can be synergistically reduced by 86 °C through the co-addition of 0.25AlH3 and 0.01CeF3. Isothermal desorption measurements demonstrate that the co-addition of AlH3 and CeF3 significantly enhances the hydrogen desorption kinetics of MgH2 with the absence of the induction period in the initial stage and the acceleration of the hydrogen desorption process. In addition, this co-doped MgH2 shows very good cycling stability at 300 °C with a 1 h capacity of 3.5 wt% and a 3 h capacity of 4.5 wt%. Structural analysis by XRD measurements indicates that during the hydrogen desorption process, MgH2 may react with Al (generated from the in situ decomposition of AlH3) to form Mg solid solution and Mg17Al12, which contribute to the thermodynamic improvement of the Mg-based material. In addition, MgH2 may also react with CeF3 to form MgF2 and CeH2–3, which act both as hydrogen diffusion gateways and as an impediment to the grain growth of MgH2 during hydrogen sorption cycling, thus improving the hydrogen desorption kinetics and the cycling stability of MgH2. Finally, it was found that the presence of AlH3 kinetically helps CeF3 to exert its positive effect on the hydrogen desorption properties of MgH2. This work provides a method for simultaneously tailoring the thermodynamic and kinetic properties of MgH2 by the synergistic addition of metal hydride and rare earth fluoride.

Remarkable hydrogen desorption properties and mechanisms of the Mg2FeH6@MgH2 core–shell nanostructure

Mg2FeH6@MgH2 dual-metal hydrides with a core–shell nanostructure were synthesized via ball-milling and heat treatment methods using Mg and Fe as raw materials assisted by diethyl ether addition. Systematic investigations of the association between the microstructure and hydrogen desorption properties of the Mg2FeH6@MgH2 core–shell hydride were performed. It is found that the as-synthesized Mg2FeH6@MgH2 is comprised of the Mg2FeH6-core with a particle size of 40–60 nm and the MgH2-shell with a thickness of 5 nm. The hydrogen desorption of the Mg2FeH6@MgH2 core–shell nanoparticle starts at 220 °C, which is ∼45 °C lower than that of the Mg2FeH6/MgH2 micrometer particle. Compared to the as-synthesized Mg2FeH6/MgH2 micrometer particle, the Mg2FeH6@MgH2 core–shell sample exhibited faster hydrogen desorption kinetics, which released more than 5.0 wt% H2 within 50 min at 280 °C. The desorption activation energy of the core–shell Mg2FeH6@MgH2 was reduced to 115.7 kJ mol−1 H2, while the desorption reaction enthalpy and entropy were calculated to be −80.6 ± 7.4 kJ mol−1 H2 and −140.0 ± 11.9 J K−1 mol−1 H2, respectively. It is proposed that the improvements of both hydrogen desorption kinetics and thermodynamics are due to the special core–shell nanostructure of Mg2FeH6@MgH2. More remarkably, it is demonstrated that the core–shell nanostructure could be recovered after rehydrogenation, leading to excellent cycling hydrogen desorption properties of Mg2FeH6@MgH2. In addition, the suggested dehydrogenation mechanism involves the dehydrogenation of the MgH2-shell followed by the decomposition of the Mg2FeH6-core into Mg and Fe according to the three-dimensional phase-boundary process.

High catalytic efficiency of amorphous TiB2 and NbB2 nanoparticles for hydrogen storage using the 2LiBH4–MgH2 system

LiBH4–MgH2 system in a 2 : 1 molar ratio constitutes a representative reactive hydride composite (RHC) for hydrogen storage. However, sluggish kinetics and poor reversibility hinder the practical applications. To ease these problems, amorphous TiB2 and NbB2 nanoparticles were synthesized and employed as catalysts for the 2LiBH4–MgH2 system. Isothermal de-/rehydrogenation and temperature programmed mass spectrometry (MS) measurements show that amorphous TiB2 and NbB2 nanoparticles can significantly improve the hydrogen storage performance of the 2LiBH4–MgH2 system. 9 wt% hydrogen can be released within only 6 min for nanoTiB2-doped 2LiBH4–MgH2, while for the undoped composite limited hydrogen of 3.9 wt% is released in 300 min at 400 °C. The dehydrogenation activation energies for the first and second steps are dramatically reduced by 40.4 kJ mol−1 and 35.2 kJ mol−1 after doping with nanoTiB2. It is believed that TiB2 and NbB2 nanoparticles can first catalyze the dehydrogenation of MgH2, and then induce the decomposition of LiBH4 and meanwhile act as nucleation agents for MgB2, thereby greatly enhancing the kinetics of dehydrogenation. The present study gives clear evidence for the significant performance of transition metal boride species in doped RHCs, which is critically important for understanding the mechanism and further improving the hydrogen storage properties of RHCs.

Electrochemical properties of La0.9Sm0.1Ni(5.0-x)Cox (x = 2.0, 2.5, 3.0) hydride electrode alloys

Abstract The electrochemical properties of La 0.9 Sm 0.1 Ni (5.0− x ) Co x ( x =2.0, 2.5, 3.0) hydride electrode alloys with and without magnetization treatment, including the electrochemical capacity C max , the charge–discharge life cycle and the high-rate dischargeability (HRD), are investigated in detail. The results show that, the effect of magnetization treatment on the electrochemical properties of the alloys studied is marked, and this effect varies with the alloy composition. After being magnetized, the electrochemical capacity of the alloys increases, the capacity decay rate decreases and the HRD improves. According to the linear polarization and anodic polarization measurements, the exchange current density I 0 and the limiting current density I L of the alloys before and after being magnetized are both found increased.

Effects of Surface Coating on the Electrochemical Properties of Amorphous CeMg12 Composite

Abstract Amorphous CeMg12 was prepared by ball milled CeMg12 alloy with Ni powder. The effects of mechanical grinding and electroless deposition of nickel (EDN) on the electrochemical properties of CeMg12 composites have been studied systematically. Amorphous CeMg12 composites have a maximum discharge capacity of 1209.6 mAh/g, but their cycling stability is poor. The cycling retention rate of the electrode is 37.26% after 10 cycles. After EDN treatment, the cycling stability of CeMg12 composite is improved markedly, and the cycling retention rate increases to 63.67% after 10 cycles. The improvement of cycling retention rate can be attributed to compact nickel coating that prevents the inner Mg from further corrosion by alkali. The nickel coating also enhances the high rate discharge (HRD) property of the composite owning to the good electrochemical catalytic properties of Ni. As oxidation and corrosion is unavoidable during EDN treatment, the maximum discharge capacity decreases slightly for CeMg12 composite with EDN treatment.